Linagliptin, chemically 8-[(3R)-3-aminopiperidin-1-yl]-7-(but-2-yn-1-yl)-3-methyl-1-[(4-methylquinazolin-2-yl)methyl]-3,7-dihydro-1H-purine-2,6-dione and has the structure formula:

Linagliptin (BI-1356) is a DPP-IV inhibitor. Linagliptin is useful for the prevention or treatment of diabetes mellitus, prediabetes or reduced glucose tolerance. The generic name linagliptin is marketed by BOEHRINGER INGELHEIM under the brand name Tradjenta®.
Linagliptin and its process were disclosed in U.S. Pat. No. 7,407,955.
Polymorphism is defined as “the ability of a substance to exist as two or more crystalline phases that have different arrangement and/or conformations of the molecules in the crystal Lattice. Thus, in the strict sense, polymorphs are different crystalline structures of the same pure substance in which the molecules have different arrangements and/or different configurations of the molecules”. Different polymorphs may differ in their physical properties such as melting point, solubility, X-ray diffraction patterns, etc. Although those differences disappear once the compound is dissolved, they can appreciably influence pharmaceutically relevant properties of the solid form, such as handling properties, dissolution rate and stability. Such properties can significantly influence the processing, shelf life, and commercial acceptance of a polymorph. It is therefore important to investigate all solid forms of a drug, including all polymorphic forms, and to determine the stability, dissolution and flow properties of each polymorphic form. Polymorphic forms of a compound can be distinguished in the laboratory by analytical methods such as X-ray diffraction (XRD), Differential Scanning calorimetry (DSC) and Infrared spectrometry (IR).
Solvent medium and mode of crystallization play very important role in obtaining one polymorphic Form over the other.
Linagliptin can exist in different polymorphic Forms, which may differ from each other in terms of stability, physical properties, spectral data and methods of preparation.
International application publication no. WO 2007/128721 disclosed Polymorph A, Polymorph B, Polymorph C, Polymorph D, Polymorph E and a mixture of Polymorph A and B of linagliptin.
Amorphous Form of linagliptin was reported in IP.com Journal (2011), 11(9A), 22.
It was observed that the crystalline Forms and amorphous Form of linagliptin either not reproducible or not stable.
We have also found a novel amorphous solid dispersion of linagliptin in combination with a pharmaceutically acceptable carrier. The amorphous solid dispersion of linagliptin is stable, reproducible and so, the amorphous solid dispersion of linagliptin is suitable for formulating linagliptin. Normally amorphous Forms are hygroscopic. Amorphous solid dispersion of linagliptin is found to be non-hygroscopic.
Thus, an object of the present invention is to provide amorphous solid dispersion of linagliptin in combination with a pharmaceutically acceptable carrier, process for its preparation and pharmaceutical compositions comprising it.